When it comes to his opinion of Apple, Elon Musk doesn't mince words.

"They have hired people we’ve fired," Musk said. "We always jokingly call Apple the 'Tesla Graveyard.' If you don’t make it at Tesla, you go work at Apple," the Tesla CEO told the German newspaper Handelsblatt last month in an article spotted by Business Insider.

Maybe the nickname was manufactured as a piece of lighthearted ribbing at a competitor's expense? Musk cleared up any ambiguity of intent, adding "I’m not kidding."

It's understandable that Musk is a little prickly when it comes to Apple, which will soon be a Tesla competitor when it launches its electric car.

If Musk is worried that the tech giant is entering his playground, he's upped his bluffing game. "Did you ever take a look at the Apple Watch?" Musk reportedly asked the interviewer, before guffawing. "No, seriously: It's good that Apple is moving and investing in this direction. But cars are very complex compared to phones or smartwatches."

Related: Elon Musk's Advice for Jack Dorsey: Don't Run Two Companies